The present invention relates to a method for promoting the recovery of effluents in a nonflowing producing zone crossed by at least one deflected well or drain, such as a petroliferous zone. What is called a deflected well or drain is any well at least part of which is substantially horizontal or little inclined in relation to the horizontal.
One of the interests of deflected wells is to allow a better sweeping of the oil effluents contained in the formations crossed and thereby to improve recovery. The sweeping mechanisms which are implemented can be natural or artificial. In the first case, the pressure necessary for the sweeping is supplied by an underlying or lateral aquifer, a volume of gaseous effluents topping the petroliferous zone or gas cap, etc. In the second case, water, steam or gas can be injected, or else pumping means can be introduced into the well.
Optimum recovery, for a given sweeping mechanism, is obtained when the sweeping front moved parallel to the deflected drain. The regularity of the sweeping front is sometimes difficult to keep because of heterogeneities of the reservoir, such as fractures or channels, etc, changes in the drain geometry or disturbances linked to the flows in the drain such as pressure drops when the production is activated by pumping, heat losses when the stimulation is carried out by a hot gaseous fluid, etc.
The influence of the temperature on the dynamic viscosity, on the density of the fluids in place in a deposit and on the phenomena taking place at the interfaces is well known, and the improvement of the production provided by the injection of a hot gaseous fluid in a drain drilled through a producing layer and fitted with regularly distributed lateral perforations and the efficiency thereof is linked to the amount of steam making through the formation.
It may be seen that the distribution of the rates of heat release along the drain is not linear.
As a matter of fact, during the first hours of injection, the reservoir, which initially shows a temperature very smaller than the temperature of the steam, is not only heated by the latent heat and part of the sensible heat of the condensed steam which has entered the reservoir zones close to the drain, but also by the heat losses, essentially by conduction, from the drain towards the reservoir. The quality of the steam consequently decreases from the inlet all along the drain.
After several hours or days of injection, according to the flow of steam injected, the cumulated amount of steam which has entered the reservoir has considerably increased the temperature in the zones close to the drain, and the thermal losses by conduction from the drain towards the reservoir are much less considerable than at the beginning of the injection. The quality of the steam in the drain thus increases in time, but it remains slightly decreasing along the drain.
During a sweeping achieved by the steam between two horizontal or subhorizontal drains, the injectable steam flows can be very low, so low that the steam at the end of the drain can be totally condensed during a large part of the sweeping process. The volume occupied by the hot water being insignificant in relation to the one occupied by the steam, the reservoir is not only heated in a non homogeneous way, but the sweeping front is irregular and the recovery of the oil in place in the region located between the two drains is not optimized.